1. Field of the Invention
The present invention relates to a bypass valve that diverts a portion of the air that has been compressed by a compressor, during the process of guiding this compressed air to a combustion chamber. The present invention further relates to a gas turbine equipped with this bypass valve.
2. Description of the Related Art
In conventional gas turbines, stable start-up operating conditions and output adjustments are designed for by diverting a portion of the air compressed by a compressor during the process of guiding this compressed air to a combustion chamber. This type of operation is carried out by means of a bypass valve that is provided along the flow path of the compressed air.
A conventional bypass valve and its surrounding structures are shown in FIG. 7. In this figure, reference number 1 indicates a combustion chamber tail pipe; 2 is a bypass pipe that is provided branching off from combustion chamber tail pipe 1; and 3 is a bypass valve provided to bypass pipe 2. A plurality of these combustion chamber tail pipes 1 is provided surrounding the perimeter of the main turbine axis, which is not shown in the figure. A bypass pipe 2 is provided for each of this plurality of combustion chamber tail pipes 1, respectively.
The structure of bypass valve 3 is schematically shown in FIG. 8. In this figure, numeric symbol 4 indicates a frame that is disposed so as to cover the end of compressed air introduction ports that are arrayed in a ring at an interval and form the bypass pipes 2; 5 is a grid plate that forms a ring shape that is identical to the array of the bypass pipes 2; 6 is an inside rail provided on the inner surface of grid plate 5 and formed in a unitary manner with frame 4; and 7 indicates a plurality of guide rollers that are provided to grid plate 5, and come into contact with inner rail 6 and assist in the rotation of grid plate 5.
A plurality of first openings 4a are formed in frame 4, these first openings 4a communicating with the end of each bypass pipe 2. A plurality of second openings 5a are formed in grid plate 5 at positions opposite first openings 4a and communicating with first openings 4a. 
In this bypass valve 3, when a tangential force is applied to grid plate 5 by an actuator, which is not shown in the figure, causing grid plate 5 to rotate, the position of second openings 5a on grid plate 5 changes relative to first openings 4a, such that the area of overlap between the two openings 4a, 5a varies. In other words, by rotating grid plate 5, it is possible to vary the amount of compressed air being bypassed for all bypass pipes 2.
During gas turbine starting and stop operations in a conventional bypass valve 3 having the design described above, smooth rotation of grid plate 5 can cease to occur due to the difference in thermal contraction that arises between frame 4 and grid plate 5. For example, during the starting operation, frame 4, which has been heated by high-temperature compressed air, can expand (thermal expansion) before grid plate 5. As a result, the guide rollers 7 on the grid plate 5 side are pressed by inner rail 6 which has expanded, and begin to contact excessively to an extent that impedes smooth rotation of grid plate 5.
Furthermore, during a stop in operation, frame 4, which is no longer being exposed to compressed air, cools down and contracts before grid plate 5. As a result, guide rollers 7 cease to be supported by inner rail 6, so that they become loose and rotation becomes unstable.
In addition, when the actuator is operated to force the grid plate to rotate when conditions for its smooth rotation are not present, it is possible to cause deformities in the grid plate.